1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which is in particular suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, and a surveillance camera, and for a silver halide camera.
2. Description of the Related Art
Zoom lenses for use in image pickup apparatuses, such as a video camera, a digital still camera, a broadcasting camera, and a surveillance camera that use a solid-state image pickup element, and a camera that uses a silver-halide film require to have a compact optical system, a high zoom ratio, and high resolution. A known example of zoom lenses that meet such requirements is a five-unit zoom lens composed of lens units having positive, negative, positive, negative, and positive refractive powers in order from the object side to the image side (U.S. Pat. No. 7,177,092). Another known example is a six-unit zoom lens composed of six lens units having positive, negative, positive, negative, positive, and negative refractive powers in order from the object side to the image side (U.S. Pat. No. 6,124,972).
Another known zoom lens has an image stabilizing performance for correcting image blur that occurs when incidental vibration is transmitted to the zoom lens due to hand shake etc. by moving part of the lens units in the direction perpendicular to the optical axis. The configuration in which a lens unit that does not move on the optical axis when zooming is used as a compensation lens unit for image stabilization can simplify the image stabilizing mechanism, which is effective in reducing the size of the zoom lens. Known examples of the zoom lens with the five unit configuration described above have an image stabilizing performance for correcting image blur by moving a fourth lens unit having negative refractive power, which does not move for zooming, in the direction perpendicular to the optical axis (U.S. Pat. Nos. 7,336,426 and 7,609,446).
In general, the amount of image blur on an image plane due to hand shake etc. is proportional to the focal length of the entire lens system. For a zoom lens, the amount of image blue is larger at the telephoto end, which requires to increase the image stabilizing correction angle at the telephoto end. Increasing the moving distance of an image stabilizing compensation lens unit in the direction perpendicular to the optical axis can increase the image stabilizing correction angle, which however causes significant eccentric aberrations, such as one-side defocusing, eccentric coma aberration, and eccentric chromatic aberration, thus degrading the image quality due to image stabilization. Therefore, in many zoom lenses, an upper limit to the image blur correction amount at the telephoto end is generally about 0.3 degrees at the field of view.
Increasing the number of lenses that constitute a compensation lens unit can further decrease such eccentric aberrations, which however increases the weight, and thus requires a large torque for electrical driving, thus increasing the size of the entire optical system. Therefore, it is important for a zoom lens having an image stabilizing performance to have a compensation lens unit with an appropriate configuration while the entire system is compact. In particular for the foregoing five-unit and six-unit zoom lenses, to maintain a high optical performance during image stabilization while reducing the size of the entire lens system, it is important to suitably set the configuration of the fourth lens unit for image stabilization and the lens units at the image side with respect to the fourth lens unit. Otherwise, it is difficult to provide a zoom lens having a high optical performance during image stabilization while reducing the size of the entire system.